Acute myeloid leukemia (AML) is a hematological malignancy characterized by the rapid growth of abnormal white blood cells that interfere with the production of normal blood cells. AML is a devastating malignancy with no approved targeted therapy, and although rare, incidence is expected to increase dramatically as the population ages. In 35% of all cases, a gain-of-function mutation occurs in the FLT3 receptor tyrosine kinase that renders the kinase constitutively active. The majority of FLT3-activating mutations occur as internal tandem duplication (ITD) events, generating an oncogene with no kinase domain regulation. The FLT3-ITD oncogene is able to transform the myeloid line of blood cells, leading to the development and progression of AML. To treat AMLs with an FLT3-ITD oncogene, the FLT3 inhibitors crenolanib and quizartinib are under clinical investigation. However, problems with both inhibitors stem from issues of toxicity and transient efficacy. With quizartinib, most patients relapse within four months of starting treatment because of inability to inhibit additional FLT3 mutations, and crenolanib causes extensive liver toxicity. Taking into account the clinical limitations of both crenolanib and quizartinib, we hypothesize that the development of a broad spectrum FLT3 mutant inhibitor that possesses an adequate safety profile will be highly efficacious in treating FLT3-ITD AML. Therefore, we propose initiating a drug discovery campaign to develop a mutation-resistant pan-FLT3 inhibitor. In parallel, we also wish to evaluate the combination of two FLT3 inhibitors with distinct mutant activity profiles in order to maintain complete FLT3 inhibition as additional mutations develop from treatment selection. This entails developing two unique compounds with mechanistically distinct FLT3 inhibitory profiles. Utilizing fragment, x-ray crystal structure, and computational-based drug discovery approaches, we will develop FLT3 inhibitor(s) for selective mutant FLT3 activity and evaluation in biochemical, cell, and mammalian-based systems for both safety and efficacy. With the completion of this study, we expect identification of a pan-FLT3 clinical candidate and/or a combination therapy of two FLT3 inhibitors. If successful, this project will positivity impact patients with FLT3-ITD AML.